<分区>
(在 .NET 4 中)创建在运行时确定的类型的实例的最佳方法是什么。
我有一个实例方法，尽管它作用于 BaseClass 对象，但它的派生类的实例可能会调用它。我需要在方法中创建另一个与 this 类型相同的实例。为每个派生类重载方法是不切实际的，因为它相当复杂，并且保持单一实现会更有效。
public class BaseClass
{
//constructors + properties + methods etc
public SomeMethod()
{
//some code
DerivedClass d = new DerivedClass(); //ideally determine the DerivedClass type at run-time
}
}
我读过一些关于反射或使用动态关键字的内容，但我没有这方面的经验。
最佳答案
在运行时重复创建实例的最佳性能方式是编译表达式:
static readonly Func<X> YCreator = Expression.Lambda<Func<X>>(
Expression.New(typeof(Y).GetConstructor(Type.EmptyTypes))
).Compile();
X x = YCreator();
统计数据(2012 年):
Iterations: 5000000
00:00:00.8481762, Activator.CreateInstance(string, string)
00:00:00.8416930, Activator.CreateInstance(type)
00:00:06.6236752, ConstructorInfo.Invoke
00:00:00.1776255, Compiled expression
00:00:00.0462197, new
统计数据(2015 年，.net 4.5，x64):
Iterations: 5000000
00:00:00.2659981, Activator.CreateInstance(string, string)
00:00:00.2603770, Activator.CreateInstance(type)
00:00:00.7478936, ConstructorInfo.Invoke
00:00:00.0700757, Compiled expression
00:00:00.0286710, new
统计数据(2015 年，.net 4.5，x86):
Iterations: 5000000
00:00:00.3541501, Activator.CreateInstance(string, string)
00:00:00.3686861, Activator.CreateInstance(type)
00:00:00.9492354, ConstructorInfo.Invoke
00:00:00.0719072, Compiled expression
00:00:00.0229387, new
完整代码:
public static X CreateY_New()
{
return new Y();
}
public static X CreateY_CreateInstance()
{
return (X)Activator.CreateInstance(typeof(Y));
}
public static X CreateY_CreateInstance_String()
{
return (X)Activator.CreateInstance("Program", "Y").Unwrap();
}
static readonly System.Reflection.ConstructorInfo YConstructor =
typeof(Y).GetConstructor(Type.EmptyTypes);
static readonly object[] Empty = new object[] { };
public static X CreateY_Invoke()
{
return (X)YConstructor.Invoke(Empty);
}
static readonly Func<X> YCreator = Expression.Lambda<Func<X>>(
Expression.New(typeof(Y).GetConstructor(Type.EmptyTypes))
).Compile();
public static X CreateY_CompiledExpression()
{
return YCreator();
}
static void Main(string[] args)
{
const int iterations = 5000000;
Console.WriteLine("Iterations: {0}", iterations);
foreach (var creatorInfo in new []
{
new {Name = "Activator.CreateInstance(string, string)", Creator = (Func<X>)CreateY_CreateInstance},
new {Name = "Activator.CreateInstance(type)", Creator = (Func<X>)CreateY_CreateInstance},
new {Name = "ConstructorInfo.Invoke", Creator = (Func<X>)CreateY_Invoke},
new {Name = "Compiled expression", Creator = (Func<X>)CreateY_CompiledExpression},
new {Name = "new", Creator = (Func<X>)CreateY_New},
})
{
var creator = creatorInfo.Creator;
var sum = 0;
for (var i = 0; i < 1000; i++)
sum += creator().Z;
var stopwatch = new Stopwatch();
stopwatch.Start();
for (var i = 0; i < iterations; ++i)
{
var x = creator();
sum += x.Z;
}
stopwatch.Stop();
Console.WriteLine("{0}, {1}", stopwatch.Elapsed, creatorInfo.Name);
}
}
public class X
{
public X() { }
public X(int z) { this.Z = z; }
public int Z;
}
public class Y : X { }
关于c# - 创建运行时确定类型实例的最佳方法，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/9788813/